There is a monitoring system (abnormality detecting device) of a conveyor belt in which a belt is provided with a transmission unit that transmits a predetermined signal to detect abnormalities in the belt which is operating, and a reception unit close to the belt receives the transmitted signal, thereby detecting the condition of the belt. In such a system, a magnetic force is generally used for the transmission unit and the reception unit (e.g., Patent Document 1). As a magnetic sensor used for the reception unit, there are many magnetic sensors such as a gauss meter, a Hall element, and a loop coil (e.g., Patent Document 2).
In addition, recently an MI sensor (magnetic impedance sensor) has been attracting attention as a low-cost and satisfactory sensitivity magnetic sensor (e.g., Patent Document 3).
The Hall element is one type of magnetic sensor using the electromagnetic conversion operation (galvanomagnetic effect operation), and generally a semiconductor of a compound with high mobility such as InSb (indium antimonide) and GaAs (gallium arsenide) is used as a raw material of the element. When a predetermined current is allowed to flow into the Hall element or a voltage is applied to the Hall element to apply a magnetic field at a right angle thereto, an electromotive force proportional to magnetic flux is generated between the output terminals.
The loop coil (search coil) is one type of magnetic sensor using the electromagnetic induction operation, and a voltage proportional to variation in time of magnetic flux interlinked to the coil is output from both ends of the coil. The loop coil outputs voltage according to variation in magnetic flux, and thus cannot detect a static magnetic field in which there is no variation in magnetic flux.
Meanwhile, the MI sensor is a sensor using a magnetic impedance effect (MI effect), and has a magnetic field detection sensitivity of 10,000 times or greater than that of the Hall element or the like. As shown in FIG. 15, the MI effect is as follows: when a pulse current with a high frequency (1 MHz or higher) generated by a high-frequency power supply 72 is allowed to flow into an amorphous magnetic metal wire 71 and a magnetic field (external magnetic field) is applied from the outside in this state, impedance of the wire 71 is drastically varied.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. S57-48521    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H08-244952    [Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2000-19235